Abstract P2-05-05: Expression profiling of in vivo DCIS progression models identified BCL9 as a molecular driver of invasive progression

Abstract

Abstract Introduction: There are an estimated 60,000 new cases of ductal carcinoma in situ (DCIS) each year. At present, it is not clear why some DCIS remain non-invasive for decades while others become invasive. A lack of understanding in DCIS pathobiology has led to overtreatment of more than half of DCIS patients. To identify factors that promote DCIS invasion, we have profiled the temporal molecular changes during DCIS transition to invasive ductal carcinoma (IDC) using two in vivo models, MIND (mouse-intraductal) and DCIS/IDC tandem lesions. These studies led to the identification of B cell lymphoma-9 as a potential molecular driver of early invasion. BCL9 is a newly found co-activator of Wnt-stimulated β-catenin-mediated transcription. BCL9 has been shown to promote progression of multiple myeloma and colon carcinoma. However its role in breast cancer progression had not been recognized. Methods: Microarray and RNA sequencing were utilized to characterize the sequential and temporal changes in mRNA expression during DCIS invasive transition. BCL9 shRNA knockdown was performed to assess the role of BCL9 in in vivo invasion, EMT and canonical Wnt signaling. Immunofluorescence of 28 patient DCIS samples was used to assess a correlation between the expression of BCL9 and biomarkers of high risk DCIS. TCGA data was analyzed to assess the status of BCL9 gene alterations in 959 human breast cancers. Results: Analysis of BCL9, by RNA and protein showed BCL9 up-regulation to be associated with DCIS transition to IDC. Analysis of patient DCIS revealed a significant correlation between high nuclear BCL9 and pathologic characteristics associated with DCIS recurrence: ER and PR negative, high nuclear grade, and high HER2. In vivo silencing of BCL9 resulted in the inhibition of DCIS invasion and reversal of epithelial-mesenchymal transition (EMT). Analysis of the TCGA data showed BCL9 gene to be altered in 26% of breast cancers. This is a significant alteration when compared to ERBB2 (19%) and ESR1 (8%). A significantly higher proportion of basal like invasive breast cancers showed BCL9 amplification. Conclusion: BCL9 is a molecular driver of DCIS invasive progression and may predispose to the development of basal like invasive breast cancers. As such, BCL9 has the potential to serve as a biomarker of high risk DCIS and as a therapeutic target for prevention of IDC. Citation Format: Behbod F, Elsarraj H, Hong Y, Valdez K, Chien J, Godwin A, Fields T. Expression profiling of in vivo DCIS progression models identified BCL9 as a molecular driver of invasive progression. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P2-05-05.